Bad customer service

On the the 27th of April I purchased a brand new acer Intel core I3 laptop at Game store Westgate mall,a few days after the laptop performance started to be slow, i called the store to let them know that I wanted to take it back as I'm not happy about how it works, they assured me that they were going to take it back, I took it back they advised me that it would take 7 working days to fix it, but to my surprise the 7days passed without them bringing it back, it was only brought back after 2 months with more problems as it is not turning on, the screen just goes blank, I've been trying to get help on returning it to get a different brand since then with no success until now I'm sitting with a R7300 laptop that I never used, can't even use it up to now due to the bad service I receive every time I reach out to the store since April. I would appreciate it I would be assisted with the way forward from here, their service has been the worst I have to say